Muscle wasting refers to the progressive loss of muscle mass and/or to the progressive weakening and degeneration of muscles, including the skeletal or voluntary muscles, which control movement, cardiac muscles, which control the heart (cardiomyopathics), and smooth muscles. Chronic muscle wasting is a chronic condition (i.e. persisting over a long period of time) characterized by progressive loss of muscle mass, weakening and degeneration of muscle.
The loss of muscle mass that occurs during muscle wasting can be characterized by a muscle protein degradation by catabolism. Protein catabolism occurs because of an unusually high rate of protein degradation, an unusually low rate of protein synthesis, or a combination of both. Muscle protein catabolism, whether caused by a high degree of protein degradation or a low degree of protein synthesis, leads to a decrease in muscle mass and to muscle wasting.
Muscle wasting is associated with chronic, neurological, genetic or infectious pathologies, diseases, illnesses or conditions. These include Muscular Dystrophies such as Duchenne Muscular Dystrophy and Myotonic Dystrophy; Muscle Atrophies such as Post-Polio Muscle Atrophy (PPMA); Cachexias such as Cardiac Cachexia, AIDS Cachexia and Cancer Cachexia, malnutrition, Leprosy, Diabetes, Renal Disease, Chronic Obstructive Pulmonary Disease (COPD), Cancer, end stage Renal failure, Sarcopenia, Emphysema, Osteomalacia, HIV Infection, AIDS, and Cardiomyopathy.
In addition, other circumstances and conditions are linked to and can cause muscle wasting. These include chronic lower back pain, advanced age, central nervous system (CNS) injury, peripheral nerve injury, spinal cord injury, chemical injury, central nervous system (CNS) damage, peripheral nerve damage, spinal cord damage, chemical damage, burns, disuse deconditioning that occurs when a limb is immobilized, long term hospitalization due to illness or injury, and alcoholism.
An intact androgen receptor (AR) signaling pathway is crucial for appropriate development of skeletal muscles. Furthermore, an intact AR-signalling pathway increases lean muscle mass, muscle strength and muscle protein synthesis.
Muscle wasting, if left unabated, can have dire health consequences. For example, the changes that occur during muscle wasting can lead to a weakened physical state that is detrimental to an individual's health, resulting in increased susceptibility to infraction and poor performance status. In addition, muscle wasting is a strong predictor of morbidity and mortality in patients suffering from cachexia and AIDS. Innovative approaches are urgently needed at both the basic science and clinical levels to prevent and treat muscle wasting, in particular chronic muscle wasting. The present invention is directed to satisfying this need.